Semiconductor device

ABSTRACT

In a semiconductor device which is assembled by making use of a lead frame  1  with a heat radiation plate  3  in which the lead frame  1  and the heat radiation plate  3  made of copper or copper alloy are joined by an adhesive layer  2  formed on a surface of the heat radiation plate  3  and at least a part of the inner leads  1   a  of the lead frame  1  is applied of a plating for a metallic fine wire connection, at least the entire portion where the lead frame  1  joins with the adhesive layer  2  is covered by at least one metal or alloy thereof different from the metallic fine wire connecting use plating selected from the group consisting of gold, platinum, iridium, rhodium, palladium, ruthenium, indium, tin, molybdenum, tungsten, gallium, zinc, chromium, niobium, tantalum, titanium and zirconium. Thereby, generation of inconveniences such as leakage and shorting due to ion migration can be prevented.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a resin molded type semiconductor device which is assembled by making use of a lead frame with a heat radiation plate.

[0003] 2. Conventional Art

[0004] These days higher integration and higher functioning of a semiconductor device are advancing and in association therewith heat amount of the semiconductor chip tends to increase. In order to dissipate heat generated by the semiconductor chip, copper or copper alloy (small amount of such as Ag, Sn, Fe, Cr, Zn, Ni, Mg, P and Si is added for enhancing such as mechanical strength) having excellent heat conductivity is currently used as the material of a lead frame in place of conventionally used 42 alloy (42% Ni—Fe alloy).

[0005] Further, since heating amount of microcomputer is particularly high, an efficient heat dissipation therefor is required, for this purpose, such as a package using a lead frame with a heat radiation plate in which the heat radiation plate is connected via an adhesive layer to the lead frame, in that HQFP (Quad Flat Package with Heat Sink) is known. FIG. 18 shows a total plane view example of a conventional HQFP, FIG. 19 shows a structure example of the conventional HQFP and FIG. 20 shows an inner plane view example of the conventional HQFP, and the conventional HQFP is generally assembled in the following manner.

[0006] At first, a heat radiation plate 3 on which an adhesive layer 2 such as polyimide resin is formed in advance such as by coating is secured to an inner lead portion 1 a of a lead frame 1 after being joined, heat pressed and cured. Subsequently, a semiconductor chip 4 is adhered on the heat radiation plate or on a die pad of the lead frame by an adhesive member 5 such as Ag paste.

[0007] Then, electrodes on the semiconductor chip and top ends of the inner lead are connected by metallic fine wires 6 such as gold. In this instance, at least a portion where the metallic fine wire of the inner lead is connected is frequently applied in advance of a plating 7 such as metallic fine wire connection use Ag so as to obtain good connectability. Thereafter, the semiconductor chip 4, the metallic fine wire 6, the inner lead 1 a and a part of or entire of the radiation plate 3 are molded by a molding resin 8 such as epoxy resin, and finally, a portion of an outer lead 1 b of the lead frame 1 is plated, bent to form the outer lead 1 b and the device is completed after being applied of marking.

[0008] Before shipping the semiconductor device into market a variety kinds of reliability tests are performed. Among these tests there is a humidity acceleration test called as PCT (Pressure Cooker Test) and when the HQFP of the conventional structure is subjected to the PCT, there arose problems that deterioration phenomena such as leakage and shorting are caused about 200 hours after starting the test.

[0009] As a result of analyzing the deterioration phenomena due to PCT by the inventors, it was found out that the causes of the deteriorations are those as will be explained below.

[0010]FIGS. 21 and 22 are A-A cross sectional view of the HQFP with a conventional structure as shown in FIG. 19, and the above problems will be explained in details with reference to FIGS. 21 and 22. FIG. 21 is the cross section before being subjected to PCT and FIG. 22 is the cross section after PCT, and the lead frame 1 is joined to the heat radiation plate 3 via the adhesive layer 2 and these are molded by the molding resin 8.

[0011] The PCT is performed at a high temperature 121° C., further since there are differences in coefficients of thermal expansion of the respective materials such as the coefficient of thermal expansion of the molding resin 8 is 10-30 ppm/° C., the coefficient of the thermal expansion of copper or copper alloy of the lead frame 1 and heat radiation plate 3 is about 17 ppm/° C. and the coefficient of thermal expansion of the adhesive layer 3 is 30-40 ppm/° C., a first problem arises, in that after PCT as shown in FIG. 22, a peeling off portion 9 is caused at respective boundaries between the lead frame 1 and the adhesive layer 2 and between the molding resin 8 and the adhesive layer 2.

[0012] Further, when the a peeling off portion 9 is caused at respective boundaries between the lead frame 1 and the adhesive layer 2 and between the molding resin 8 and the adhesive layer 2, since the PCT is performed under a severe condition of 121° C./100% RH/2 atm, moisture penetrates into the semiconductor device through the boundary between the lead frame 1 and the molding resin 8 or through the molding resin 8 itself, and the moisture collects inside the peeling off portion 9.

[0013] In to the moisture collected in the peeling off portion 9 components of such as the molding resin 8, the adhesive layer 2 and the paste material 5 are extracted and the collected moisture shows acidic. The extracted components are organic acid and chlorine ions contained in the molding material or a component which changes the extracted liquid into acid.

[0014] By this acidic solution the copper or the copper alloy which is the material of the lead frame 1 is eluted and ionized, and is redeposited as deposited copper 10, thereby, a phenomenon (ion migration) of a second problem of shorting between leads arises.

[0015] Further, at the top end portion of the inner lead 1 a where the plating 7 such as Ag for connecting the metallic fine wire 6, the plating metal 7 and the copper or the copper alloy which is the material of the lead frame 1 are exposed to the moisture at the same time, a galvanic cell is formed by the dissimilar metal junction and the above phenomenon is further accelerated.

[0016]FIGS. 23 and 24 show around the end portion (B portion) of the heat radiation plate 3 in the HQFP with the conventional structure as shown in FIG. 19. FIG. 23 shows B portion before PCT and FIG. 24 shows B portion after PCT respectively, the lead frame 1 is joined to the heat radiation plate 3 via the adhesive layer 2 and these are molded by the molding resin 8.

[0017] Even at a heat radiation plate end portion 3 a the peeling off portion 9 is likely caused after PCT as shown in FIG. 24 and moisture accumulates at the peeling off portion 9. By this accumulated acidic water the copper or the copper alloy which is the material of the heat radiation plate 3 is eluted and ionized, redeposited as the deposited copper 10, thereby, a problem of causing shorting phenomenon between the lead frame 1 and the heat radiation plate 3 arises.

[0018] Further, JP-A-10-163410 (1998) proposes an ion migration preventing method in a taping lead frame in which a protective film is formed at a portion of a lead contacting to an adhesive.

[0019] However, an object of JP-A-10-163410 (1998) is to prevent copper diffusion movement through the adhesive in the taping lead frame by the electric field formed by voltage application, the structure of the concerned lead frame with the heat radiation plate and the semiconductor device, and ion migration phenomenon are different.

[0020] Further, the ion migration of the copper diffusive movement through the adhesive is resolved by changing the adhesive material from phenol resin series to such as maleimide resin series and polyimide resin series.

[0021] Further, JP-A-8-20498 (1996) proposes a lead frame with a heat radiation plate in which, in order to prevent electrical shorting between the lead frame and the heat radiation plate end portion due to heat radiation plate punching burr, an insulative coating is provided for the lead frame at the face joining to the adhesive layer and the insulative coating is formed so as to protrude from the heat radiation plate end portion.

[0022] However, with this measure, when the concerned peeling off is caused, the migration between leads and between a lead and a heat radiation plate can not be prevented.

[0023] In particular, JP-A-8-204098 (1996) nowhere discloses migration between the leads.

[0024] Accordingly, for example, when dealing a narrow pitch type semiconductor device of which interlead pitch is narrow, the technical countermeasure to the migration disclosed in JP-A-8-204098 (1996) is insufficient.

SUMMARY OF THE INVENTION

[0025] An object of the present invention is to solve the above first and second problems and to provide a semiconductor device which limits generation of peeling offs and cracks and prevents inconvenience such as leakage and shorting due to ion migration even when the peeling offs and cracks are caused.

[0026] The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the attached drawings.

[0027] Among inventions disclosed in the present application, an outline of typical ones are briefly explained herein below.

[0028] Namely, a semiconductor device according to one aspect of the present invention comprises a plurality of inner leads which are made of copper or copper alloy and extend around a semiconductor chip, a heat radiation plate which joins to one ends of the plurality of inner leads via an insulative adhesive layer and on which the semiconductor chip is mounted via the adhesive layer or an adhesive different from the adhesive layer, a plurality of metallic fine wires which connect between the semiconductor chip and the plurality of inner leads respectively and a molding resin which molds the semiconductor chip, the plurality of metallic fine wires and the heat radiation plate, wherein a portion of the inner leads which joins with the adhesive layer is covered by a metal having higher reference electrode potential than that of copper.

[0029] Further, a semiconductor device according to another aspect of the present invention wherein a lead frame and a heat radiation plate which are made of copper or copper alloy are joined by an adhesive layer formed on a surface of the heat radiation plate, the device is assembled by making use of the lead frame with the heat radiation plate of which at least a part of inner leads are applied of a metallic fine wire connection use plating and at least the entire portion where the lead frame joins with the adhesive layer is covered by at least one metal or alloy different from the metallic fine wire connecting use plating selected from the group consisting of gold, platinum, iridium, rhodium, palladium, ruthenium, indium, tin, molybdenum, tungsten, gallium, zinc, chromium, niobium, tantalum and titanium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is an enlarged partial cross sectional view of a structure example of a semiconductor device (HQFP) representing embodiment 1 of the present invention;

[0031]FIG. 2 is an enlarged partial cross sectional view of a structure example of a semiconductor device (HQFP) representing embodiment 2 of the present invention;

[0032]FIG. 3 is an enlarged partial cross sectional view of a structure example of a semiconductor device (HQFP) representing embodiment 3 of the present invention;

[0033]FIG. 4 is an enlarged partial cross sectional view of a structure example of a semiconductor device (HQFP) representing embodiment 4 of the present invention;

[0034]FIG. 5 is an enlarged partial cross sectional view of a structure example of a semiconductor device (HQFP) representing embodiment 5-13 of the present invention;

[0035]FIG. 6 is an enlarged partial cross sectional view of a structure example of a semiconductor device (HQFP) representing embodiment 14 of the present invention;

[0036]FIG. 7 is an evaluation diagram showing humidity resistance evaluation of embodiments 1-14 and comparative example (FIGS. 20 and 21) obtained by PCT (Pressure Cooker Test);

[0037]FIG. 8 is a plane view of a structure example of a semiconductor device (HQFP) of the present invention;

[0038]FIG. 9 is a cross sectional view showing a structure of the semiconductor device as shown in FIG. 8;

[0039]FIG. 10 is a plane view showing an inner structure of the semiconductor device (HQFP) as shown in FIG. 8;

[0040]FIG. 11 is an enlarged partial cross sectional view of a structure example of a semiconductor device (HQFP) representing embodiment 15 of the present invention;

[0041]FIG. 12 is a cross sectional view showing a BGA structure of a semiconductor device representing embodiment 16 of the present invention;

[0042]FIG. 13 is a cross sectional view showing a packaged structure of the BGA as shown in FIG. 12;

[0043]FIG. 14 is a plane view showing an inner structure of the BGA shown in FIG. 12;

[0044]FIG. 15 is a cross sectional view showing a cross sectioned structure taken along E-E line as shown in FIG. 14;

[0045]FIG. 16 is an enlarged partial cross sectional view showing F portion structure shown in FIG. 15;

[0046]FIG. 17 is a cross sectional view showing a BGA structure of a semiconductor device representing embodiment 17 of the present invention;

[0047]FIG. 18 is an entire plane view of a semiconductor device (HQFP) using a conventional lead frame with heat radiation plate;

[0048]FIG. 19 is a cross sectional view showing a structure of the semiconductor device (HQFP) using the conventional lead frame with a heat radiation plate;

[0049]FIG. 20 is a plane view of an inner structure of the semiconductor device (HQFP) using the conventional lead frame with a heat radiation plate;

[0050]FIG. 21 is an enlarged partial cross sectional view showing A-A cross section in FIG. 19;

[0051]FIG. 22 is an enlarged partial cross sectional view showing a structure of the cross section of FIG. 21 after PCT;

[0052]FIG. 23 is an enlarged partial cross sectional view showing a portion (B portion) around the end portion of the heat radiation plate in FIG. 19;

[0053]FIG. 24 is an enlarged partial cross sectional view showing a structure after PCT of the cross section as shown in FIG. 23; and

[0054]FIG. 25 is an enlarged partial cross sectional view showing a structure example, of Pb free solder packaging by Pd plating over entire lead surface of a semiconductor device (HQFP) of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Hereinbelow, embodiments of the present invention will be explained in detail with reference to the drawings. At first embodiments 1 through 14 will be explained with reference to the drawings. For the convenience of the explanation, a comparative example for the first time will be explained for clarifying advantages of the embodiments 1 through 14, subsequently, structures of the embodiments 1-8 which resolve the second problem will be explained, then, the structure of the embodiments 9 through 14 which resolve the first problem will be explained, and finally advantages of the embodiments 1 through 14 will be explained by making use of “humidity resistance evaluation result” as shown in FIG. 7.

COMPARATIVE EXAMPLES

[0056] As comparative examples for demonstrating advantages of the embodiments 1 through 14 which will be explained hereinbelow, conventional examples as shown in FIGS. 21 and 23 are used. In FIG. 21, there is no metallic coating 11 as shown in FIG. 1 formed by such as plating at the junction portion between a lead frame 1 and an adhesive layer 2, and copper or copper alloy which is a material for the lead frame 1 is left in a state as exposed, and in FIG. 23 there is no metallic coating 11 as shown in FIG. 1 such as by plating at a heat radiation plate end portion 3 a, and copper or copper alloy which is a material for the heat radiation plate 3 is left in a state as exposed.

[0057] (Embodiment 1)

[0058] At first, a structure of HQFP 13 as shown in FIGS. 8 and 9 will be explained which is an example of a semiconductor device according to the present invention and which is constituted by a semiconductor chip 4 on which semiconductor integrated circuits are formed, a plurality of inner leads which are constituted by copper or copper alloy and are disposed in an extending manner around the semiconductor chip 4, a heat radiation plate 3 which is constituted by copper or copper alloy and is joined with one ends (chip side end portions) of the plurality of inner leads 1 a via the insulative adhesive layer 2 and on which the semiconductor chip 4 is mounted via the adhesive layer 2 or an adhesive member (adhesive) 5, a plurality of metallic fine wires which connect the semiconductor chip 4 with respective inner leads 1 a, a molding resin 8 which molds the semiconductor chip 4, the plurality of metallic fine wires 6 and the heat radiation plate 3 and a plurality of outer leads 1 b which are formed integral with the respective inner leads 1 a and are produced outside from the molding resin 8 while being bent in a gull wing shape and a metallic coatings 11 are formed at portions where the plurality of inner leads 1 a are joined with the respective adhesive layer 2.

[0059] Further, the region where the metallic coatings 11 are formed at the respective inner leads 1 a is a metallic coating region 12 as shown in FIG. 10 which covers all of the regions where boundaries formed between the molding resin 8, inner leads 1 a and the adhesive layer 2 in which peeling off is possibly caused, and covers a region on the respective inner leads joined with the adhesive layer 2 which is slightly outward near from the chip side end portions.

[0060] Further, on the respective inner leads 1 a at the connecting portions with the metallic fine wires 6 Ag platings 7 used for connection with the metallic fine wire 6 are applied.

[0061] Further, the semiconductor chip 4 is secured on the adhesive layer 2 by the adhesive member 5 such as Ag paste.

[0062] Herein, FIG. 1 shows a cross sectional view of a semiconductor device of embodiment 1 according to the present invention which makes use of a lead frame with a heat radiation plate and shows an enlarged cross section taken along C-C in FIG. 9. As shown in FIG. 1, by applying Au plating over the all of the portions of the lead frame 1 which is to be joined with the adhesive layer 2 the metallic coating 11 is formed. For the plating, any methods such as an electro plating and an electro less plating can be used.

[0063] Further, the metal coating 11 can be formed other than plating such as by physical vapor deposition including vacuum evaporation, spattering and ion plating and by chemical vapor deposition. After forming the metallic coating, the heat radiation plate 3 on which the adhesive layer 2 is formed beforehand is adhered to the lead frame 1 to thereby obtain a lead frame with a heat radiation plate. An assembly of the semiconductor device thereafter is performed according to a conventional processes.

[0064] Namely, after preparing the lead frame with a heat radiation plate, the semiconductor chip 4 is die-bonded via the adhesive member 5 on the adhesive layer 2 of the heat radiation plate 3 serving as a die pad (chip mounting portion) for the lead frame with a heat radiation plate, thereafter, the semiconductor chip 4 is wire-bonded to the respective inner leads 1 a by the metallic fine wires 6.

[0065] Subsequently, cutting of the outer leads 1 b is performed as well as the same are bent in a gull wing shape to complete assembling of the HQFP 13.

[0066] (Embodiment 2)

[0067]FIG. 2 shows a cross sectional view of a semiconductor device of embodiment 2 according to the present invention which makes use of a lead frame with a heat radiation plate and shows an enlarged cross section taken along C-C in FIG. 9. As shown in FIG. 2, by applying Au plating over the all of the portions of the lead frame 1 which is to be joined with the adhesive layer 2 the metallic coating 11 is formed. After forming the metallic coating, the heat radiation plate 3 on which the adhesive layer 2 is formed beforehand is adhered to the lead frame 1 to thereby obtain a lead frame with a heat radiation plate. An assembly of the semiconductor device thereafter is performed according to a conventional processes.

[0068] (Embodiment 3)

[0069]FIG. 3 shows a cross sectional view surrounding the heat radiation plate end portion of a semiconductor device of embodiment 3 according to the present invention which makes use of a lead frame with a heat radiation plate and shows an enlarged cross section of D portion in FIG. 9. As shown in FIG. 3, by applying Au plating over the heat radiation plate end portion 3 a beforehand, the metallic coating 11 is formed. After forming the metallic coating, the heat radiation plate 3 on which the adhesive layer 2 is formed beforehand is adhered to the lead frame 1 to thereby obtain a lead frame with a heat radiation plate. An assembly of the semiconductor device thereafter is performed according to a conventional processes.

[0070] (Embodiment 4)

[0071]FIG. 4 shows a cross sectional view surrounding the heat radiation plate end portion of a semiconductor device of embodiment 3 according to the present invention which makes use of a lead frame with a heat radiation plate and shows an enlarged cross section of D portion in FIG. 9. As shown in FIG. 4, by applying Au plating over the entire circumference of the heat radiation plate 3 beforehand, the metallic coating 11 is formed. After forming the metallic coating, on one surface of the heat radiation plate 3 the adhesive layer 2 is formed, therefore the same is adhered to the lead frame 1 to thereby obtain a lead frame with a heat radiation plate. An assembly of the semiconductor device thereafter is performed according to a conventional processes.

[0072] (Embodiment 5)

[0073]FIG. 5 shows a cross sectional view surrounding the heat radiation plate end portion of a semiconductor device of embodiment 5 according to the present invention which makes use of a lead frame with a heat radiation plate and shows an enlarged cross section taken along C-C in FIG. 9. As shown in FIG. 5, by applying Au plating over all of the portions of the lead frame 1 which is to be joined with the adhesive layer 2 the side portions of the lead and the entire surrounding of the heat radiation plate 3, the metallic coating 11 is formed. After forming the metallic coating, on one surface of the heat radiation plate 3 the adhesive layer 2 is formed, thereafter the same is adhered to the lead frame 1 to thereby obtain a lead frame with a heat radiation plate. An assembly of the semiconductor device thereafter is performed according to a conventional processes.

[0074] (Embodiments 6-13)

[0075] The structures of these embodiments are the same as that of FIG. 5 embodiment 5, however, different from embodiment 5 wherein Au plating is applied, the entire portion of the lead frame 1 which is joined to the adhesive layer 2 and the entire circumference of the heat radiation plate 3 are applied by Pt plating (Embodiment 6), Rh plating (Embodiment 7), Pd plating (Embodiment 8), Sn plating (Embodiment 9), Zn plating (Embodiment 10), Cr plating (Embodiment 11), Ni plating (Embodiment 12) and Ti plating (Embodiment 13), thereby, the metal coating 11 is formed. After forming the metallic coating, on one surface of the heat radiation plate 3 the adhesive layer 2 is formed, thereafter the same is adhered to the lead frame 1 to thereby obtain a lead frame with a heat radiation plate. An assembly of the semiconductor device thereafter is performed according to a conventional processes.

[0076] (Embodiment 14)

[0077]FIG. 6 shows a cross sectional view surrounding the heat radiation plate end portion of a semiconductor device of embodiment 5 according to the present invention which makes use of a lead frame with a heat radiation plate and shows an enlarged cross section taken along C-C in FIG. 9. As shown in FIG. 6, by applying polyimide resin vanish over all of the portions of the lead frame 1 which is to be joined with the adhesive layer 2 and the entire surrounding of the heat radiation plate 3, and after drying the same the insulative coating 11 is formed. Other than the polyimide resin, another insulative resin such as phenol, epoxy and polyamide can be used for the insulative coating 11.

[0078] Further, in order to improve heat conductivity and to match thermal expansion coefficient with other members of the insulative coating 11, an inorganic material such as alumina and silica can be mixed into the insulative resin as a filler. After forming the insulative coating, on one surface of the heat radiation plate 3 the adhesive layer 2 is formed, thereafter the same is adhered to the lead frame 1 to thereby obtain a lead frame with a heat radiation plate. An assembly of the semiconductor device thereafter is performed according to a conventional processes.

[0079] (Humidity Resistance Evaluation Result)

[0080]FIG. 7 shows an evaluation result of PCT (Pressure Cooker Test) performed for evaluating humidity resistance. The test condition of the PCT was 121°/100% RH/2 atm.

[0081] As shown in FIG. 7, with regard to the comparative example on a conventional HQFP, after about 200 hours when the PCT has been started, a peeling off was caused (first problem) and a shorting poor between leads and between lead and heat radiation plate was caused (second problem). In contrast thereto, according to the embodiments 1-14, a good result was obtained, in that the shorting poor is rarely caused or never caused in comparison with the comparative example. Now, the respective humidity resistance evaluation results of the embodiments 1-14 will be explained in more detail.

[0082] With regard to embodiments 1 and 2, a peeling off was caused after about 200 hours when the PCT has been started like the comparative example. However, no migration between leads was caused. Although since the heat radiation plate end portion 3 a was not coated, a migration between lead and heat radiation plate was caused after about 300 hours from the start of the PCT.

[0083] With regard to embodiments 3 and 4, a peeling off was also caused after about 200 hours when the PCT has been started like the comparative example. Further, since no coating was applied over the lead frame, a migration between leads was caused like the comparative example. However, a migration between lead and heat radiation plate was reduced in comparison with the comparative example. However, the migration can not be completely prevented.

[0084] With regard to embodiment 5, a peeling off was caused after about 200 hours when the PCT has been started like the comparative example. However, no migration between leads and between lead and heat radiation plate was caused.

[0085] With regard to embodiments 6 through 8, a peeling off was caused after about 200 hours when the PCT has been started like the comparative example. However, since the concerned portions of the lead frame are coated by one of platinum, rhodium and palladium which is hardly eluted by acidic water content like gold, no migration was caused, as well as no shorting poor between leads and between lead and heat radiation plate was caused.

[0086] As has been explained above, with the embodiments 1-8 the second problem was resolved.

[0087] With regard to embodiments 9 and 10, a peeling off was caused after 300 hours when the PCT has been started. Because the surface of the lead frame was coated by tin or zinc, it is considered that the adhesive force thereby with the adhesive was increased in comparison with that by copper. Further, even after a peeling off was caused, because the tin shows a better anti acid elution property than copper or although the zinc surface is corroded the zinc is never eluted in a form of ions, no migration was induced and no shorting poor between leads and between lead and heat radiation plate was induced.

[0088] With regard to embodiments 11 and 12, no peeling off was caused after 400 hours when the PCT has been started. Because the surface of the lead frame was coated by chromium or nickel, it is considered that the adhesive force thereby with the adhesive was increased in comparison with that by copper. Further, even after a peeling off was caused, because the chromium and nickel are hardly eluted under acidic water environment than copper, no migration was induced and no shorting poor between leads and between lead and heat radiation plate was induced.

[0089] With regard to embodiment 13, no peeling off was caused after 500 hours when the PCT has been started. Because the surface of the lead frame was coated by titanium, it is considered that the adhesive force thereby with the adhesive was increased in comparison with that by copper. Further, even after a peeling off was caused, because on the surface of the titanium a passivated coating anti acid resistance is formed which prevents elution thereof. Therefore, no migration was induced and no shorting poor between leads and between lead and heat radiation plate was induced.

[0090] With regard to embodiment 14, a peeling off was caused after 400 hours when the PCT has been started. Although, after 500 hour when PCT has started a slight peeling off of the sample has caused, the peeling off has induced between the insulative coating 11 made of polyimide resin and the adhesive layer, but no peeling off between the lead frame 1 and the insulative coating 11 and between the heat radiation plate 3 and the insulative coating 11 has been induced. It is considered that the adhesive force of the insulative coating 11 is high which is formed by coating polyimide resin vanish over a metal such as copper and by drying the same. Therefore, no migration was induced and no shorting poor between leads and between lead and heat radiation plate was induced.

[0091] As has been explained above, with the embodiments 9 through 14, the first problem as well as the second problem can be resolved.

[0092] (Embodiment 15)

[0093]FIG. 11 shows a structure of embodiment 15 and shows an enlarged cross section of D portion in FIG. 9.

[0094] Namely, at the surrounding edge portion of the heat radiation plate a bent portion 3 a is formed which is bent in a direction separating away from the inner lead 1 a, of which structure is combined with such as FIG. 1 embodiment 1 structure and FIG. 2 embodiment 2 structure.

[0095] With such combined structure, since a gap between the inner lead 1 a and the heat radiation plate end portion 3 a, a possible Cu migration generation between the lead and the heat radiation plate is prevented.

[0096] Namely, with the structures of FIGS. 1 and 2, although the number of shorting poor between leads is zero but a shorting between lead and heat radiation plate has occurred as shown in the humidity resistance evaluation in FIG. 7, however, when the structure as shown in FIG. 11 is combined with the structure of either FIG. 1 or FIG. 2, the shorting between the lead and the heat radiation plate can be prevented with the simple structure.

[0097] Further, as the metallic coating 11 formed on the inner lead 11 a as has been explained in connection with the embodiments 1 through 15, when a combination of substrate nickel (Ni) plating and entire surface palladium plating is used, an armor plating or Ag plating at the top end of the inner lead can be omitted, thereby, the manufacturing process thereof can be simplified.

[0098] Namely, as shown in FIG. 25, through the use of the Pd plating 22, wettability with leads of the solder which is used when actually packaging the HQFP 13 on a wiring substrate 20 can be ensured, thereby, the conventional armor plating process performed at the top end of the outer lead 1 b can be omitted as well as a structure (Pb free structure) can be realized which does not need to use Pb which was used conventionally for the outer lead 1 b.

[0099] In particular, when a Pb freed semiconductor device is intended, as shown in FIG. 25, when the HQFP 13 which uses a lead frame 1 of which inner lead 1 a and outer lead 1 b are applied at the same time of the Pd plating is packaged on the wiring substrate 20 by connecting the same to the substrate side terminals 20 a via Pb free solder 21, migration prevention between Cu leads as well as Pb freed semiconductor device can be realized at the same time.

[0100] Further, through the use of the Pd plating, the connectability of the portions on the inner leads 1 a where the metallic fine wires 6 are connected is ensured, thereby, the conventional Ag plating 7 for connection with the metallic fine wires which was performed for the inner leads 1 a can be omitted.

[0101] Further, when tin (Sn) plating is used for the metallic coating 11 formed on the inner leads 1 a, it is possible to perform a wire bonding directly on the tin (Sn) plating after breaking the oxide film on the surface.

[0102] Accordingly, a metallic coating 11 serving as an armor plating can be formed, a process of omitting conventional armor plating can be achieved as well as Pb free process can be realized.

[0103] (Embodiment 16)

[0104] A semiconductor device of embodiment 16 as shown in FIG. 12 is a BGA (Ball Grid Array) 16, and is constituted by a wiring substrate 14 having a plurality of copper foil leads 14 a, a semiconductor chip 4 disposed on an chip supporting face 14 b of the wiring substrate 14, a plurality of metallic fine wires (a metallic bump can do) 6 which electrically connect the semiconductor chip 4 with respective copper foil leads 14 a, a molding resin 8 which molds the semiconductor chip 4, the plurality of metallic fine wires 6 and the plurality of copper foil leads 14 a and a plurality of ball electrodes (projection electrodes) 15 which are provided on a back face 14 c at the side opposite to the face where the copper foil leads 14 a of the wiring substrate 14 are formed, and at least on portions of the copper foil leads 14 c which are covered by the molding resin 8 a metallic coating 11, for example, such as gold is formed as shown in FIG. 16.

[0105] Namely, the BGA 16 of the present embodiment is structured in such a manner that on the chip supporting surface 14 b of the wiring substrate 14 the plurality of copper leads 14 a are formed as shown in FIGS. 14 and 15, further, the respective copper foil leads 14 a are covered by an insulative solder resist films 14 e except for the connecting region with the metallic fine wires 6 substantially the entire portion on the side of chip supporting face 14 b including the copper foil leads 14 a and the solder resist film 14 e is covered by the molding resin 8.

[0106] Accordingly, the BGA 16 is structured in such a manner that, as shown in FIG. 16, each surface of the copper leads 14 a is covered by respective separate metallic coatings 11 such as gold plating, on the upper layer thereof an insulative solder resist film 14 e and further, on the solder resist film 14 e the molding resin 8 are respectively disposed.

[0107] Further, the wiring substrate 14 is, for example, an epoxy resin substrate containing glass fibers and BT (Bismalemide triazine) substrate, and as shown in FIG. 12, through wiring passing through through-holes formed in the wiring substrate 14 the copper foil leads 14 a disposed on the chip supporting face 14 b are electrically connected to the ball electrodes 15 on the back face 14 c thereof.

[0108] Further, FIG. 13 shows a packaging structure of the BGA 16 on the package substrate 17.

[0109] Since the BGA 16 is a high heat dissipation type semiconductor device in which the heat radiation plate 3 is attached at the side of back face 14 c of the wiring substrate 14, the ball electrodes 15 contact with the substrate side terminals 17 a as well as the heat radiation plate 3 contacts with the substrate side terminals 17 a via the solder junction portion 18, thereby, the heat dissipation property is enhanced.

[0110] According to the BGA 16 of embodiment 16, since the metallic coating 11 is formed on the surface of the copper foil leads 14, when water content inside the substrate swells because of moisture absorption and a peeling off between the copper foil lead 14 a and the solder resist film 14 e or between the copper foil lead 14 a and the molding resin 8, deposition of Cu ions can be prevented, and like the embodiments 1 through 15, with the present embodiment the second problem or both the first and second problems can be resolved.

[0111] (Embodiment 17)

[0112] A semiconductor device of embodiment 17 as shown in FIG. 17 is a small size BGA (Ball Grid Array) 19 and has a structure in which as the wiring substrate 14 a tape substrate constituted by such as a thin film polyimide tape is used.

[0113] In the BGA 19, the metal coating 11 having the same structure as shown in FIG. 16 is formed on the surface of the copper foil leads 14 a, therefore, like the embodiments 1-15 the second problem or both the first and second problems can be resolved.

[0114] Further, as materials of the metallic coating 11 formed on the inner lends 1 a or the copper foil leads 14 a as has been explained in connection with embodiments 1-17, any metals which hardly cause Cu migration can be used.

[0115] Metals which are applicable to the present invention for forming the metallic coating 11 are ones having a higher reference electrode potential than copper (Cu), for example, such as gold (Au), platinum (Pt), iridium (Ir), rhodium (Rh), palladium (Pd) and silver (Ag), and at least not less than one of these metals and their alloys can be used for the metallic coating 11.

[0116] Further, metals which form passivation films under acidic condition can also be used, these are ruthenium (Ru), indium (In), tin (Sn), molybdenum (Mo), tungsten (Ta), gallium (Ga), zinc (Zn), chromium (Cr), niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), osmium (Os) aluminum (Al), hafnium (Hf) and nickel (Ni), and at least not less than one of these metals and their alloys can be used for the metallic coating 11.

[0117] Hitherto, inventions invented by the inventors are specifically explained with reference to the embodiments, however, it is needless to say that the present inventions should not be limited to the embodiments and can be modified in a variety of manners within the scope not exceeding the gist of the present invention.

[0118] For example, in the embodiments 1-15 the HQFP was explained, however the applicable object of the present invention should not be limited to the HQFP type semiconductor device with a heat radiation plate having high thermal conductivity in view of the heat dissipation property of the semiconductor device, for example, the present invention is applicable to a QFP type semiconductor device with a substrate, in which when the width of an inner lead top end becomes fine in association with pin number increasing and pitch size reducing, the mechanical strength of the top and of the inner lead during resin molding process is ensured by securing the top end of the inner leads on the substrate.

[0119] For the above explained structure, the migration counter measure to Cu leads of the present invention can be applied, when there is a thermal expansion coefficient difference between the substrate and the molding resin and a peeling off at the boundary between the substrate and the molding resin is possibly caused due to the difference.

[0120] Typical advantages of the present invention as disclosed above will be briefly explained.

[0121] Since the surface of the inner leads which are joined to the heat radiation plate via the adhesive layer and the surface of the heat radiation plate are coated by the metallic coating such as gold, the adhesive strength between the inner leads and the adhesive layer, the inner leads and the molding resin and the heat radiation plate and the molding resin is increased, thereby, a generation rate of peeling offs and cracks can be reduced when being subjected to PCT. Further, even when the peeling off and crack are caused, the surfaces of the inner leads and the heat radiation plate at the peeling off boundary are coated by a metallic coating such as gold and others or by an insulation coating, the migration of copper or copper alloy can be prevented, thereby, a highly reliable semiconductor device free from leakage and shorting problems can be obtained. Further, because of no migration occurrence, a high density semiconductor device with further microscopic lead pitch can be obtained. 

1. A semiconductor device comprising: a semiconductor chip; a plurality of inner leads which are made of copper or copper alloy and extend around a semiconductor chip; a heat radiation plate which joins to one ends of the plurality of inner leads via an insulative adhesive layer and on which the semiconductor chip is mounted via the adhesive layer or an adhesive different from the adhesive layer; a plurality of metallic fine wires which connect between the semiconductor chip and the plurality of inner leads respectively; and a molding resin which molds the semiconductor chip, the plurality of metallic fine wires and the heat radiation plate, wherein a portion of the inner leads which joins with the adhesive layer is covered by a metal having higher reference electrode potential than that of copper.
 2. A semiconductor device of claim 1, wherein the metals having higher reference electrode potential than that of copper are at least one among the group consisting of gold, platinum, iridium, rhodium, palladium and silver or an alloy thereof.
 3. A semiconductor device comprising: a semiconductor chip; a plurality of inner leads which are made of copper or copper alloy and extend around a semiconductor chip; a heat radiation plate which joins to one ends of the plurality of inner leads via an insulative adhesive layer and on which the semiconductor chip is mounted via the adhesive layer or an adhesive different from the adhesive layer; a plurality of metallic fine wires which connect between the semiconductor chip and the plurality of inner leads respectively; and a molding resin which molds the semiconductor chip, the plurality of metallic fine wires and the heat radiation plate, wherein an end portion of the heat radiation plate is covered by a metal having higher reference electrode potential than that of copper.
 4. A semiconductor device comprising: a semiconductor chip; a plurality of inner leads which are made of copper or copper alloy and extend around a semiconductor chip; a heat radiation plate which joins to one ends of the plurality of inner leads via an insulative adhesive layer and on which the semiconductor chip is mounted via the adhesive layer or an adhesive different from the adhesive layer; a plurality of metallic fine wires which connect between the semiconductor chip and the plurality of inner leads respectively; and a molding resin which molds the semiconductor chip, the plurality of metallic fine wires and the heat radiation plate, wherein a portion of the inner leads which joins with the adhesive layer and an end portion of the heat radiation plate are covered by a metal having higher reference electrode potential than that of copper.
 5. A semiconductor device comprising: a semiconductor chip; a plurality of inner leads which are made of copper or copper alloy and extend around a semiconductor chip; a heat radiation plate which joins to one ends of the plurality of inner leads via an insulative adhesive layer and on which the semiconductor chip is mounted via the adhesive layer or an adhesive different from the adhesive layer; a plurality of metallic fine wires which connect between the semiconductor chip and the plurality of inner leads respectively; and a molding resin which molds the semiconductor chip, the plurality of metallic fine wires and the heat radiation plate, wherein a portion of the inner leads which joins with the adhesive layer is covered by a metal which forms a passivation film under acidic condition.
 6. A semiconductor device of claim 5, wherein the metals which form a passivation film under acidic condition are at least one among ruthenium, indium, tin, molybdenum, tungsten, gallium, zinc, chromium, niobium, tantalum, titanium, zirconium, osmium, aluminum, hafnium and nickel or an alloy thereof.
 7. A semiconductor device comprising: a semiconductor chip; a plurality of inner leads which are made of copper or copper alloy and extend around a semiconductor chip; a heat radiation plate which joins to one ends of the plurality of inner leads via an insulative adhesive layer and on which the semiconductor chip is mounted via the adhesive layer or an adhesive different from the adhesive layer; a plurality of metallic fine wires which connect between the semiconductor chip and the plurality of inner leads respectively; and a molding resin which molds the semiconductor chip, the plurality of metallic fine wires and the heat radiation plate, wherein an end portion of the heat radiation plate is covered by a metal which forms a passivation film under acidic condition.
 8. A semiconductor device comprising: a semiconductor chip; a plurality of inner leads which are made of copper or copper alloy and extend around a semiconductor chip; a heat radiation plate which joins to one ends of the plurality of inner leads via an insulative adhesive layer and on which the semiconductor chip is mounted via the adhesive layer or an adhesive different from the adhesive layer; a plurality of metallic fine wires which connect between the semiconductor chip and the plurality of inner leads respectively; and a molding resin which molds the semiconductor chip, the plurality of metallic fine wires and the heat radiation plate, wherein a portion of the inner leads which joins with the adhesive layer and an end portion of the heat radiation plate are covered by a metal which forms a passivation film under acidic condition.
 9. A semiconductor device of claim 1, wherein around the circumferential edge portion of the heat radiation plate a bent portion is formed which is bent in a direction separating away from the inner leads.
 10. A semiconductor device of claim 5, wherein around the circumferential edge portion of the heat dissipation plate a bent portion is formed which is bent in a direction separating away from the inner leads.
 11. A semiconductor device which is assembled by making use of a lead frame with a heat radiation plate in which the lead frame and the heat radiation plate made of copper or copper alloy are joined by an adhesive layer formed on a surface of the heat radiation plate and at least a part of the inner leads of the lead frame is applied of a plating for a metallic fine wire connection, comprising: a semiconductor chip mounted on the heat radiation plate or on a die pad of the lead frame metallic fine wires which electrically connect the inner leads with the semiconductor chip and a molding resin which molds the semiconductor chip, characterized in that at least the entire portion where the lead frame joins with the adhesive layer is covered by at least one metal or alloy different from the metallic fine wire connecting use plating selected from the group consisting of gold, platinum, iridium, rhodium, palladium, ruthenium, indium, tin, molybdenum, tungsten, gallium, zinc, chromium, niobium, tantalum, titanium and zirconium.
 12. A semiconductor device which is assembled by making use of a lead frame with a heat radiation plate in which the lead frame and the heat radiation plate made of copper or copper alloy are joined by an adhesive layer formed on a surface of the heat radiation plate and at least a part of the inner leads of the lead frame is applied of a plating for a metallic fine wire connection, comprising: a semiconductor chip mounted on the heat radiation plate or on a die pad of the lead frame metallic fine wires which electrically connect the inner leads with the semiconductor chip and a molding resin which molds the semiconductor chip, characterized in that at least an end portion of the heat radiation plate is covered by at least one metal or alloy selected from the group consisting of gold, platinum, iridium, rhodium, palladium, ruthenium, indium, tin, molybdenum, tungsten, gallium, zinc, chromium, niobium, tantalum, titanium and zirconium.
 13. A semiconductor device which is assembled by making use of a lead frame with a heat radiation plate in which the lead frame and the heat radiation plate made of copper or copper alloy are joined by an adhesive layer formed on a surface of the heat radiation plate and at least a part of the inner leads of the lead frame is applied of a plating for a metallic fine wire connection, comprising: a semiconductor chip mounted on the heat radiation plate or on a die pad of the lead frame metallic fine wires which electrically connect the inner leads with the semiconductor chip and a molding resin which molds the semiconductor chip, characterized in that at least the entire portion where the lead frame joins with the adhesive layer and at least an end portion of the heat radiation plate are covered by at least one metal or alloy different from the metallic fine wire connecting use plating selected from the group consisting of gold, platinum, iridium, rhodium, palladium, ruthenium, indium, tin, molybdenum, tungsten, gallium, zinc, chromium, niobium, tantalum, titanium and zirconium.
 14. A semiconductor device which is assembled by making use of a lead frame with a heat radiation plate in which the lead frame and the heat radiation plate made of copper or copper alloy are joined by an adhesive layer formed on a surface of the heat radiation plate and at least a part of the inner leads of the lead frame is applied of a plating for a metallic fine wire connection, comprising: a semiconductor chip mounted on the heat radiation plate or on a die pad of the lead frame metallic fine wires which electrically connect the inner leads with the semiconductor chip and a molding resin which molds the semiconductor chip, characterized in that at least the entire portion where the lead frame joins with the adhesive layer is covered by an insulative coating.
 15. A semiconductor device which is assembled by making use of a lead frame with a heat radiation plate in which the lead frame and the heat radiation plate made of copper or copper alloy are joined by an adhesive layer formed on a surface of the heat radiation plate and at least a part of the inner leads of the lead frame is applied of a plating for a metallic fine wire connection, comprising: a semiconductor chip mounted on the heat radiation plate or on a die pad of the lead frame metallic fine wires which electrically connect the inner leads with the semiconductor chip and a molding resin which molds the semiconductor chip, characterized in that at least an end portion of the heat radiation plate is covered by an insulative coating.
 16. A semiconductor device which is assembled by making use of a lead frame with a heat radiation plate in which the lead frame and the heat radiation plate made of copper or copper alloy are joined by an adhesive layer formed on a surface of the heat radiation plate and at least a part of the inner leads of the lead frame is applied of a plating for a metallic fine wire connection, comprising: a semiconductor chip mounted on the heat radiation plate or on a die pad of the lead frame metallic fine wires which electrically connect the inner leads with the semiconductor chip and a molding resin which molds the semiconductor chip, characterized in that at least the entire portion where the lead frame joins with the adhesive layer and at least an end portion of the heat radiation plate are covered by an insulative coating.
 17. A semiconductor device comprising: a wiring substrate including a plurality of copper foil leads; a semiconductor chip disposed on an upper portion of the wiring substrate; a plurality metallic fine wires or metallic bumps which electrically connect the semiconductor chip with the respective plurality of copper foil leads; a molding resin which molds the semiconductor chip, the plurality of metallic wires or metallic bumps and the plurality of copper foil leads; and a plurality of projecting electrodes which are provided on a face of the wiring substrate opposite from the face where the plurality of copper foil leads are formed, characterized in that at least a portion of the copper foil leads which are covered by the molding resin is coated by a metal having higher reference electrode potential than that of copper.
 18. A semiconductor device of claim 17, wherein the metals having higher reference electrode potential than that of copper are at least one among the group consisting of gold, platinum, iridium, rhodium, palladium and silver or an alloy thereof.
 19. A semiconductor device comprising: a wiring substrate including a plurality of copper foil leads; a semiconductor chip disposed on an upper portion of the wiring substrate; a plurality metallic fine wires or metallic bumps which electrically connect the semiconductor chip with the respective plurality of copper foil leads; a molding resin which molds the semiconductor chip, the plurality of metallic wires or metallic bumps and the plurality of copper foil leads; and a plurality of projecting electrodes which are provided on a face of the wiring substrate opposite from the face where the plurality of copper foil leads are formed, characterized in that at least a portion of the copper foil leads which are covered by the molding resin is coated by a metal which forms a passivation film under acidic condition.
 20. A semiconductor device of claim 19, wherein the metals which form a passivation film under acidic condition are at least one among ruthenium, indium, tin, molybdenum, tungsten, gallium, zinc, chromium, niobium, tantalum, titanium, zirconium, osmium, aluminum, hafnium and nickel or an alloy thereof. 